This invention relates generally to integrated circuit (IC) packages.
In ball grid array (BGA) IC packages, there are generally two types of pads to which a BGA ball is electrically coupled, non-solder mask defined (NSMD) pads and solder mask defined (SMD) pads. Some of the main disadvantages of NSMD pads are pad lifting and poor routing capability. Due to their smaller metal pad size, SMD pads provide finer routing capability than NSMD pads. Additionally, SMD pads arc not subject (or are less susceptible) to pad lifting as the end portions of their metal pads are covered by dielectric layers. However, SMD pads have worse solder joint reliability (SJR) than NSMD pads. The SJR worsens as the substrate thickness of the IC package is reduced. With sufficient thinning of the core substrate, an SMD pad may fail to meet SJR specifications. For example, it appears that SMD pads may not meet SJR specifications if used with 400 micrometer core substrates. Similarly, core-less IC packages similarly suffer from low SJR.